This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-355010 filed on Nov. 20, 2001, Japanese Patent Application No. 2001-363119 filed on Nov. 28, 2001, Japanese Patent Application No. 2001-363142 filed on Nov. 28, 2001 and Japanese Patent Application No. 2001-372540 filed on Dec. 6, 2001.
1. Field of the Invention
The present invention relates to an intake control system of an internal combustion engine, the intake control system being capable of controlling quantity of intake air for each cylinder by controlling opening and closing of intake control valves disposed in intake passages of the engine.
2. Description of Related Art
Conventionally, a known intake control system, which is provided with intake control valves disposed in intake passages of an internal combustion engine, controls quantity of intake air for each cylinder by controlling opening and closing of the intake control valves respectively, besides a throttle valve disposed in the engine.
In such a kind of intake control system, the intake control valves disposed in the intake passages of the respective cylinders are capable of being controlled to open and to close by actuators respectively and independently. Therefore, it is possible to prevent back flow of intake air, which occurs in an intake stroke when an engine revolution is in a low speed range, by controlling the opening and closing timing of the intake control valves in correspondence with operating conditions of the engine. As a result, an output of the engine is improved. In addition, it is possible to reduce a pumping loss, which increases when the engine is under a partial load especially when the engine is idling, by controlling the opening and closing timing of the intake control valves in correspondence with operating conditions of the engine. Thus, fuel consumption is reduced, as is commonly known. When the engine is under a partial load, especially when the engine is idling, intake air is drawn through one port alone. Therefore, swirls or tumbles are generated in the cylinder and atomization of fuel is improved. Accordingly, the fuel is mixed with air efficiently, and fuel combustion is improved.
Conventionally, a 90-degree rotating type rotary solenoid actuator, an R/S actuator, is used as an actuator that drives the intake control valve to open and to close. The R/S actuator holds the intake control valve at a neutral position where an intake passage is half opened, when current is not supplied thereto. When the current is supplied, the R/S actuator drives the intake control valve from the neutral position to a direction to open or to close the intake control valve in correspondence with strength and direction of the current.
In such a case in which the R/S actuator that holds the intake control valve at the neutral position when the current is not supplied thereto is employed, safety is ensured because the engine is capable of operating without closing the intake passage even if the current is not supplied to the R/S actuator because of a breakdown and the like. In addition, the opening and closing directions of the intake control valve are changed by altering the direction of the current supply. Therefore, the intake control valve is capable of being driven from a full opening position to a full closing position quickly, and vice versa.
However, when the R/S actuator is used to control the opening and closing of the intake control valve, the R/S actuator needs the current supply invariably even when the intake control valve is held at a full opening position and the opening and closing control is not performed. As a result, power consumption is increased.
As a solution for such a problem, Japanese Patent Laid-Open Publication No. H06-58192 discloses an intake control system that reduces the power consumption by reducing current supply to an R/S actuator while an intake valve is closed, as intake characteristics of an engine are not affected even if the intake control valve is opened or closed while the intake valve is closed.
FIG. 8A is a longitudinal cross-sectional view showing an intake control device of the conventional intake control system and FIG. 8B is a cross-sectional view showing the intake control device along the line VIIIBxe2x80x94VIIIB in FIG. 8A. The conventional R/S actuator 20 that controls the intake control valve 10 comprises a support shaft 21, a magnetic member 22, electromagnetic coils 23, 24, permanent magnets 25, 26 and the like as shown in FIGS. 8A and 8B. The support shaft 21 connected with a support shaft 11 of the intake control valve 10 is held in a casing 27 rotatably. The magnetic member 22 is press-fitted around the support shaft 21 and is formed with opposing magnetic poles symmetrically in a radial direction. The pair of electromagnetic coils 23, 24 are disposed on inner walls of the casing 27, facing each other across the magnetic member 22. The pair of permanent magnets 25, 26 are disposed on the inner walls of the casing 27 so that the permanent magnets 25, 26 face each other across the magnetic member 22, and the alignment thereof is perpendicular to that of the electromagnetic coils 23, 24.
When the electromagnetic coils 23, 24 are supplied with current, the magnetic member 22 is rotated to a position determined by magnetic poles provided by the electromagnetic coils 23, 24 and magnetic poles provided by the permanent magnets 25, 26. As a result, the support shaft 21 integrated with the magnetic member 22 is rotated, and the intake control valve 10 is rotated from a neutral position, a half opening position, toward a full opening position or a full closing position.
If the current supply to the electromagnetic coils 23, 24 is cut off, the magnetic member 22 is attracted by the magnetic poles of the permanent magnets 25, 26 alone. Accordingly, the intake control valve 10 is rotated to the neutral position and is stabilized there.
As explained above, the conventional R/S actuator 20 is a permanent magnet type torque motor. The permanent magnets 25, 26 for holding the rotor 21 at the neutral position are disposed in the stator of the conventional R/S actuator 20. The magnetic member 22 is disposed around the rotor 21. The rotor 21 is rotated by supplying current to the electromagnetic coils 23, 24 and is rotated from the half opening position to the full closing position or the full opening position.
Generally, mechanical inertia of its motor should be small because the R/S actuator for controlling the opening and closing of the intake control valve has to operate quickly. Therefore, large magnets are not applicable in the motor, and large torque is not acquired even if the current is supplied. Accordingly, when the rotor of the motor is held at a full closing position or at a full opening position, large current is required to hold the rotor, because a torque constant, torque generated per unit current, is small. As a result, reduction of the power consumption is not attainable.
In addition, the conventional R/S actuator uses detent torque when returning to the neutral position. Therefore, improvement of its response cannot be expected. Moreover, there are some more disadvantages, such as a high-cost, because the permanent magnets are used in the stator.
Japanese Patent Laid Open Publication H04-292528 discloses another intake control system that controls intake control valves by R/S actuators. The intake control system controls quantity of intake air by opening and closing the intake control valves once in every intake stroke in compliance with a command from an electronic control unit (ECU). However, the intake control system is not provided with sensors such as an opening degree sensor or a coil temperature sensor. Therefore, the intake control system is controlled in an open loop control and is only capable of performing the intake control with timing that is programmed in advance. Accordingly, the intake control system is not capable of regulating quantity of intake air by controlling the intake control valves at the optimum timing. As a result, reduction of the fuel consumption and improvement of the output of the engine are not attained sufficiently.
The intake control system disclosed in Japanese Patent Laid Open Publication H04-292528 basically closes the intake control valve in an early stage of an intake stroke as shown in FIG. 16 to reduce pumping loss caused when the engine is under a partial load, especially when the engine is idling. In FIG. 16, a broken line (f) represents an operation of the exhaust valve and a solid line (g) represents an operation of the intake valve, and a line (h) represents an operation of the intake control valve. PO represents the full opening position and PC represents the full closing position of the intake control valve.
However, in a scheme explained above, in order to reduce the pumping loss, the intake control valve is operated to open and to close once in one cycle of the engine, synchronized with the cycle of the engine, as shown in FIG. 16. The intake control valve is open during an overlapping period xe2x80x9cTOLxe2x80x9d in which the intake valve and the exhaust valve, which are driven by high-speed cams having profiles adapted for high-speed, are open together. Accordingly, exhaust gas could flow back into an intake passage especially when the engine is under a partial load. As a result, the fuel combustion is deteriorated and the fuel consumption is increased.
It is therefore an object of the present invention to provide an intake control system of an internal combustion engine, wherein the intake control system improves response and reduces power consumption.
It is another object of the present invention to provide an intake control system of an internal combustion engine, wherein the intake control system improves controlling accuracy of intake control valves and controls quantity of intake air at optimum timing so that fuel consumption is reduced and output of the engine is improved.
It is also another object of the present invention to provide an intake control system of an internal combustion engine, wherein the intake control system reduces pumping loss in an intake stroke and prevents exhaust gas from flowing back into intake passages to prevent deterioration of fuel combustion and to reduce fuel consumption.
According to an aspect of the present invention, an intake control system of an internal combustion engine comprises intake control valves disposed in respective cylinders of the engine and rotary solenoid actuators, R/S actuators, that control the intake control valves to open and to close. A stator and a rotor of the R/S actuator provide air gaps therebetween and the air gaps change length thereof in a rotational direction of the rotor. A plurality of electromagnetic coils are disposed in the stator so that magnetic flux is generated mainly through the air gaps formed from the rotor to a direction in which the rotor is to be rotated among the air gaps. A spring is connected with a support shaft of the intake control valve and holds the intake control valve at a neutral position, a half opening position, when the R/S actuator is not supplied with the current. Thus, the intake control system that has a high response and is capable of reducing the power consumption is provided.
According to another aspect of the present invention, a stator of an R/S actuator of an intake control system has a plurality of electromagnetic coils disposed in four radial directions from a rotor in an interval of generally 90 degrees. The electromagnetic coils generate magnetic flux mainly in a pair of quarter spaces across the rotor in the stator when the electromagnetic coils are supplied with the current. The spaces where the magnetic flux is generated are rotated by changing the directions of the current supplied to the electromagnetic coils. Thus, holding force to hold the intake control valve at a full closing position or at a full opening position is easily acquired. And thus, the stator and the rotor attract and stick to each other directly in direction of rotation of the rotor. As a result, the response of the intake control valve is improved and the power consumption is reduced.
According to another aspect of the present invention, an intake control valve of an intake control system is opened after an exhaust valve is closed so that the intake control valve is not opened in an overlapping period in which an intake valve and the exhaust valve are open together. Accordingly, exhaust gas is prevented from flowing back into an intake passage and destabilization of fuel combustion is prevented. Moreover, the intake control valve is closed before the intake valve is closed. Therefore, a spit back of fresh air, a flowing back of intake air, is prevented.
According to another aspect of the present invention, an intake control system of an internal combustion engine calculates a target operation timing of an opening and closing operation of intake control valves with using a map and based on an accelerator opening degree and rotation speed of the engine. In addition, the intake control system calculates an error between the target operation timing and an actual operation timing detected by opening degree sensors disposed in the intake control valves, and operates the intake control valves in the next opening and closing operation at the operation timing of which error is corrected. Thus, variation in the actual operations is inhibited, and quantity of the intake air is controlled at the suitable timing. As a result, the fuel consumption is reduced and the output of the engine is improved. Moreover, the intake control system is not provided with a main control valve for controlling the entire intake air. The intake control system is provided with the intake control valves disposed in the respective cylinders. Therefore, the intake control system is capable of controlling the intake air precisely per each cylinder.
According to another aspect of the present invention, an intake control system performs a first opening and closing control and a second opening and closing control of the intake control valve in a cycle of an engine. In the first opening and closing control, after an overlapping period of an intake valve and an exhaust valve ends, the intake control valve is driven from a full closing position to a full opening position, and after necessary intake air is drawn, the intake control valve is driven from the full opening position to the full closing position before the intake valve closes. In the second opening and closing control, after the intake valve closes, the intake control valve is driven from the full closing position to the full opening position, and after the pressure in an intake passage becomes the atmospheric pressure, the intake control valve is driven from the full opening position to the full closing position before the intake valve opens. Thus, the intake control valve opens when the exhaust valve is closed after the overlapping period ends, and therefore, exhaust gas is prevented from flowing back into the intake passage. As a result, deterioration of fuel combustion is prevented. In addition, the intake control valve is opened momentarily after the intake valve is closed so that the intake stroke starts after the pressure in the intake passage is atmospheric pressure. As a result, pumping loss is reduced.